A memory device is proposed in which memory cells are aligned three dimensionally by forming a memory hole in a stacked body having a plurality of electrode layers functioning as a control gate in a memory cell and a plurality of insulating layers stacked alternately, forming a charge storage film on a side wall of the memory hole, and then providing silicon serving as a channel in the memory hole.
Furthermore, in the memory device, a U-shaped memory string structure is proposed which has a pair of columnar parts extending in a stacking direction of the stacked body including the plurality of layers of electrode layers, and a joint part embedded in a back gate and linking the pair of columnar parts.
Before forming the stacked body including electrode layers, a depression part is formed in a underlying layer serving as a back gate, and a sacrifice film is embedded in the depression part. After that, the stacked body including electrode layers is formed on the underlying layer, and then a hole in the columnar parts is formed to thereby remove the sacrifice film in the depression part by etching through the hole. That is, in forming a U-shaped memory hole, there are included a process of forming a depression part, a process of embedding a sacrifice film in the depression part, and further a process of flattening a surface of a underlying layer by removing a sacrifice film other than the depression part.